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Date:   Mon, 9 Mar 2020 11:51:20 -0700
From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Maulik Shah <mkshah@codeaurora.org>, evgreen@chromium.org,
        mka@chromium.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, agross@kernel.org,
        dianders@chromium.org, rnayak@codeaurora.org, ilina@codeaurora.org,
        lsrao@codeaurora.org,
        Mahesh Sivasubramanian <msivasub@codeaurora.org>,
        devicetree@vger.kernel.org
Subject: Re: [PATCH v4 1/4] dt-bindings: Introduce SoC sleep stats bindings
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On Mon 09 Mar 11:23 PDT 2020, Stephen Boyd wrote:

> Quoting Maulik Shah (2020-03-09 04:14:14)
> > From: Mahesh Sivasubramanian <msivasub@codeaurora.org>
> > 
> > Add device binding documentation for Qualcomm Technologies, Inc. (QTI)
> > SoC sleep stats driver. The driver is used for displaying SoC sleep
> > statistic maintained by Always On Processor or Resource Power Manager.
> > 
> > Cc: devicetree@vger.kernel.org
> > Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>
> > Signed-off-by: Lina Iyer <ilina@codeaurora.org>
> > Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
> > Reviewed-by: Rob Herring <robh@kernel.org>
> > Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> > ---
> >  .../bindings/soc/qcom/soc-sleep-stats.yaml         | 46 ++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/soc/qcom/soc-sleep-stats.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/soc/qcom/soc-sleep-stats.yaml b/Documentation/devicetree/bindings/soc/qcom/soc-sleep-stats.yaml
> > new file mode 100644
> > index 00000000..7c29c61
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/soc/qcom/soc-sleep-stats.yaml
> > @@ -0,0 +1,46 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/soc/qcom/soc-sleep-stats.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Qualcomm Technologies, Inc. (QTI) SoC sleep stats bindings
> > +
> > +maintainers:
> > +  - Maulik Shah <mkshah@codeaurora.org>
> > +  - Lina Iyer <ilina@codeaurora.org>
> > +
> > +description:
> > +  Always On Processor/Resource Power Manager maintains statistics of the SoC
> > +  sleep modes involving powering down of the rails and oscillator clock.
> > +
> > +  Statistics includes SoC sleep mode type, number of times low power mode were
> > +  entered, time of last entry, time of last exit and accumulated sleep duration.
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - qcom,rpmh-sleep-stats
> > +      - qcom,rpm-sleep-stats
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +
> > +examples:
> > +  # Example of rpmh sleep stats
> > +  - |
> > +    rpmh_sleep_stats@c3f0000 {
> > +      compatible = "qcom,rpmh-sleep-stats";
> > +      reg = <0 0xc3f0000 0 0x400>;
> > +    };
> > +  # Example of rpm sleep stats
> > +  - |
> > +    rpm_sleep_stats@4690000 {
> 
> Node names don't have underscores. It really feels like we should be able
> to get away with not having this device node at all. Why can't we have
> the rpm message ram be a node that covers the entire range and then have
> that either create a platform device for debugfs stats or just have it
> register the stat information from whatever driver attaches to that
> node?
> 
> Carving this up into multiple nodes and making compatible strings
> doesn't seem very useful here because we're essentially making device
> nodes in DT for logical software components that exist in the rpm
> message ram.

It's been a while since I discussed this with Lina, but iirc I opted for
the model you suggest and we concluded that it wouldn't fit with the RPM
case.

And given that, for reasons unknown to me, msgram isn't a single region,
but a set of adjacent memory regions, this does seem to represent
hardware better.

Regards,
Bjorn